8/8/07 Look for Sudden Death Syndrome (SDS) In Minnesota Soybean Fields - UMN Extension Crop enews
Sudden death syndrome (SDS) is a fungal disease of soybeans caused by Fusarium solani f.sp. glycines, and has caused substantial soybean yield reductions in states south of Minnesota. The disease has spread northward over the last couple of decades. Although SDS has not been confirmed in Minnesota (as of the spring of 2001) there were two unconfirmed reports of SDS in the summer of 2000.
One report was a field in Goodhue County and the second was in Olmstead County (Figure1). The likelihood that SDS is present in Minnesota is great, considering the disease is already found in the bordering states of Iowa and Wisconsin.
Soybean yield losses from SDS can range from only slight to 100%. Actual yield loss depends on when plants become infected. The earlier the infection occurs the greater the severity of the disease and the greater the loss. SDS is often first observed infesting round or elliptical patches in fields (Figure 2). Over time the infested area can spread through the entire field (Figure 3).
Disease symptoms usually appear after flowering and during pod fill. Typical foliar symptoms of SDS begin, as small chlorotic spots on leaves (Figure 4). The spots coalesce until the entire intervenal tissue of leaf is chlorotic. The chlorosis progresses to necrosis giving the leaves a fired look (Figure 5). The dead interveinal tissue falls from the leaf giving the leaf a tattered appearance (Figure 6). The leaf veins remain green and the leaves often drop off the plant leaving bare petioles still attached to the plant stems (Figure 7).
Foliar symptoms progress quickly, thus the name “sudden death.” In severely infected plants, the roots are rotted near the crown, and plants can be easily pulled from the soil. The outer cambial tissue of SDS infected stems exhibit rot but the stem’s pith remains white (Figure 8). The causal agent of SDS, Fusarium solani f.sp. glycines, produces slow-growing blue colored fungal colonies with macroconidia on infected roots about 10 cm below the soil surface (Figure 9). The blue colonies sometimes can be observed with the naked eye. Since other Fusarium species can produce blue colonies also, the colonies are not definitive of the SDS pathogen.
Foliar symptoms of closely resemble those of brown stem root (BSR), a common disease of Minnesota soybeans. BSR can easily be mistaken for SDS. One way to distinguish between the two diseases is to examine the cambium and pith of infected stems. Stems of BSR infected plants have brown discoloration of the pith particularly in the region of the nodes. The vascular tissue of SDS infected plants can turn reddish brown but the pith remains white. Foliar and root symptoms can be used to identify SDS but positive identification is best made by a qualified plant disease clinic.
Positive Identification of Sudden Death Syndrome (SDS)
SDS and brown stem rot of soybeans have similar symptoms but the control measures are different for the two diseases so proper diagnosis is important. If you suspect SDS send whole infected soybean plants to a plant disease clinic for identification.
The address of the University of Minnesota Plant Disease Clinic is:
495 Borlaug Hall;
1991 Upper Buford Circle
St. Paul, MN 55108.
Questions about sample submission can be addressed by calling the clinic at (612) 625-1275. Information about the clinic and sample submission can be found on the web at http://pdc.umn.edu/
Samples are diagnosed for a minimal charge.
Cool, wet weather early in the growing season favors the initial infection of soybeans by the fungus. Disease development can be most severe in poorly drained soils. No-till production favors SDS disease development more so than conventional tillage. This is probably at least partially due to greater moisture retention, compaction, and slower warming of the soil in the spring in no-till fields. Warm, dry conditions at or after flowering contribute to foliar symptom development when soybean plants are under moisture stress. The pathogen overwinters in soybean debris and in the soil. There may be an association between SDS and the soybean cyst nematode (SCN). Fields with SCN are prime candidates for SDS.
Although SDS has not been confirmed in Minnesota, utilizing known SDS management techniques may reduce the chances of developing SDS in the near future. Many of the management practices for SDS are simply good production practices for soybeans. Management of SDS includes modifying cultural practices and using resistant varieties. Delaying soybean planting, moldboard tillage, and increasing soil drainage will reduce the incidence of the disease. No-till production of soybeans should be avoided in poorly drained soils. There are SDS resistant soybean varieties, some of which also have resistance for SCN. Properly managing SCN with resistant varieties and rotations to non-host crops will help manage SDS.
We greatfully acknowledge the following researchers for the use of their images on this page.
Figures 2 and 7, courtesy of the American Phytopathological Society. Hartman, G.L., G.R. Noel, and L.E. Gray. 1995. Occurrence of soybean sudden death syndrome in east-central Illinois and associated yield losses. Plant Disease 79:314-318
Figures 3-6, and 9, courtesy of Dr. X.B. Yang. More of Dr. Yang’s extensive collection of crop disease symptom photos can be viewed at http://www.ent.iastate.edu/imagegal/plantpath/
Figure 8, courtesy of Dr. Patrick Lipps, The Ohio State University. Additional crop disease symptoms can be viewed at: http://cfaes.osu.edu:90/ClipArt/